1. Field of the Invention
The present invention relates to a gear unit apparatus for a printer, and particularly to a gear unit apparatus for a printer, which rotary drives various rollers such as a platen roller or a transfer roller in a thermal printer.
2. Description of Related Art
In a conventional printer (e.g., a thermal printer), a printing paper such as a label, a tag or the like is sandwiched between a thermal head and a platen roller to transfer the printing paper by rotary driving the platen roll, and predetermined printing data is supplied to the thermal head to print information having a predetermined content onto the printing paper.
Moreover, in order to assist in the transfer of a relatively large printing paper, an auxiliary transfer roller (transfer roller) is disposed on an upstream side of the platen roller, or a board-extension roller (transfer roller) is provided for pulling only a board that is turned around in a releasing section in order to release the label from the board.
A group of various belts (timing belts) and a group of gears are used as the rotary driving force of a drive motor in order to rotary drive the various rollers (the transfer rollers such as the platen roller, auxiliary transfer roller and board-extension roller) in a direction of transferring the printing paper, but when these rollers wear out, the group of belts that is engaged with the group of gears needs to be removed once in order to exchange the rollers, deteriorating the replacement workability.
Moreover, these groups of belts and gears are generally provided on the reverse bracket within the printer housing, and removal and replacement of the various rollers are performed by opening and closing the printer cover, thus it is definitely not easy to replace the rollers. For this reason, the problem is that time and effort are involved in a maintenance check, negatively affecting the maintenance characteristics of the printer.
Since the various rollers are rotary driven by the drive motor via the groups of belts and gears, and because of a gap between the gears (backlash of the gears), it is difficult to ensure the position to start printing and the accuracy of the transfer control, and it is also difficult to improve the performance of the printer.
In addition, when it is necessary to change the print density in accordance with the information to be printed or the contents of a print design in a printing section, the print head needs to be switched to a thermal head that has different print dot density, and the speed of printing the printing paper also needs to be changed, thus the speed of transferring the printing paper by means of the drive motor is also changed.
However, if it is difficult to take a measurement for changing/correcting the printing speed and the transfer speed using only software by means of a print controller, it is necessary to mechanically change the groups of belts and gears by changing the route of the group of belts, requiring new assembly work in order to make such changes.
It should be noted that the tension of the group of belts combined with the group of gears needs to adjusted, but if the group of belts are embedded particularly within a narrow space of the printer main body, it is difficult to carry out the adjustment work.